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  Fast Math: sin/cos lookup tables  (Read 3910 times)
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Offline Riven
« League of Dukes »

JGO Overlord


Medals: 781
Projects: 4
Exp: 16 years


Hand over your head.


« Posted 2011-05-09 20:27:55 »

Math.sin() is slow. Using a lookup table for sin/cos is roughly 50x faster. The loss of accuracy is minimal, maximum error is roughly 0,001. You can probably get away with it.

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   public static final float sin(float rad)
   {
      return sin[(int) (rad * radToIndex) & SIN_MASK];
   }

   public static final float cos(float rad)
   {
      return cos[(int) (rad * radToIndex) & SIN_MASK];
   }

   public static final float sinDeg(float deg)
   {
      return sin[(int) (deg * degToIndex) & SIN_MASK];
   }

   public static final float cosDeg(float deg)
   {
      return cos[(int) (deg * degToIndex) & SIN_MASK];
   }

   private static final float   RAD,DEG;
   private static final int     SIN_BITS,SIN_MASK,SIN_COUNT;
   private static final float   radFull,radToIndex;
   private static final float   degFull,degToIndex;
   private static final float[] sin, cos;

   static
   {
      RAD = (float) Math.PI / 180.0f;
      DEG = 180.0f / (float) Math.PI;

      SIN_BITS  = 12;
      SIN_MASK  = ~(-1 << SIN_BITS);
      SIN_COUNT = SIN_MASK + 1;

      radFull    = (float) (Math.PI * 2.0);
      degFull    = (float) (360.0);
      radToIndex = SIN_COUNT / radFull;
      degToIndex = SIN_COUNT / degFull;

      sin = new float[SIN_COUNT];
      cos = new float[SIN_COUNT];

      for (int i = 0; i < SIN_COUNT; i++)
      {
         sin[i] = (float) Math.sin((i + 0.5f) / SIN_COUNT * radFull);
         cos[i] = (float) Math.cos((i + 0.5f) / SIN_COUNT * radFull);
      }

      // Four cardinal directions (credits: Nate)
     for (int i = 0; i < 360; i += 90)
      {
         sin[(int)(i * degToIndex) & SIN_MASK] = (float)Math.sin(i * Math.PI / 180.0);
         cos[(int)(i * degToIndex) & SIN_MASK] = (float)Math.cos(i * Math.PI / 180.0);
      }
   }

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Offline Nate

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Projects: 4
Exp: 14 years


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« Reply #1 - Posted 2011-05-10 04:25:55 »

Thanks Riven, I used code based on this in libgdx. I found in practice that it is important to have correct values for the 4 cardinal directions:
http://code.google.com/p/libgdx/source/browse/trunk/gdx/src/com/badlogic/gdx/math/MathUtils.java#43

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